Textural and Geochemical Evolution

Crystallographic texture and microstructural changes in fusion welds of recrystallized Zry-4 rolled plates

We use an Earth system model of intermediate complexity, CLIMBER‐2, to investigate what recent improvements in the representation of the physics and biology of the glacial ocean imply for the atmospheric concentration. The coupled atmosphere‐ocean model under the glacial boundary conditions is able to reproduce the deep, salty, stagnant water mass inferred from Antarctic deep pore water data and the changing temperature of the entire deep ocean. When carbonate compensation is included in the model, we find a CO2 drawdown of 43 ppmv associated mainly with the shoaling of the Atlantic thermohaline circulation and an increased fraction of water masses of southern origin in the deep Atlantic. Fertilizing the Atlantic and Indian sectors of the Southern Ocean north of the polar front leads to a further drawdown of 37 ppmv. Other changes to the glacial carbon cycle include a decrease in the amount of carbon stored in the terrestrial biosphere (540 Pg C), which increases atmospheric CO2 by 15 ppmv, and a change in ocean salinity resulting from a drop in sea level, which elevates CO2 by another 12 ppmv. A decrease in shallow water CaCO3 deposition draws down CO2 by 12 ppmv. In total, the model is able to explain more than two thirds (65 ppmv) of the glacial to interglacial CO2 change, based only on mechanisms that are clearly documented in the proxy data. A good match between simulated and reconstructed distribution of δ13C changes in the deep Atlantic suggests that the model captures the mechanisms of reorganization of biogeochemistry in the Atlantic Ocean reasonably well. Additional, poorly constrained mechanisms to explain the rest of the observed drawdown include changes in the organic carbon:CaCO3 ratio of sediment rain reaching the seafloor, iron fertilization in the subantarctic Pacific Ocean, and changes in terrestrial weathering.

Optimierung der Eigenschaften von neuartigem Elektrobandstahl

The influence of varying substrate temperature, N2 partial pressure, ion energy, and ion-to-Ti flux ratio on the texture development and mechanical properties of TiN is investigated in detail. We show that during low substrate temperature (T s = 300 °C) reactive sputtering of TiN in a mixed Ar + N2 discharge a change from 111- to 001-oriented growth occurs when increasing the ion-to-Ti ratio J i/J Ti above 2.5 while using a low ion energy E i of 30 eV. This texture change can be reversed to a 111-oriented growth by increasing the ion energy to 60 and 90 eV when using high ion-to-Ti ratios J i/J Ti of 2.5 and 9, without introducing strain. Thereby the hardness can be increased from ∼31 to 37 GPa with only minor changes in compressive stresses. Consequently, by defining the ion-to-Ti ratio and the ion energy during low substrate temperature reactive sputtering of TiN the texture development towards 111- or 001-oriented growth can be controlled. Based on previous studies and the texture development as a function of substrate temperature and N2-partial pressure, we propose that varying the ion-to-Ti ratio and the ion energy result in different N-terminated surfaces and hence different Ti-fluxes from 111- to 001-oriented grains and vice versa.

Sediment cores collected from different locations of Lake Umbozero were studied with respect to concentration and mobility of trace and heavy metals Co, Cu, Fe, Mn, Ni, Pb, U, and Zn. Lake Umbozero is the second largest lake in the Murmansk Region and subjected to contamination by air-borne emissions and river transportation from the nearby metallurgical and mining industries. Unlike its neighboring, more industry-prone Lake Imandra, Lake Umbozero is relatively unexplored with respect to its state of pollution. In our study, metal distribution in sediments was found to vary with respect to the cores, although in general the concentrations were at the same level throughout the lake indicating uniform horizontal distribution of metals. When compared to Lake Imandra, the concentrations of most of the metals studied were significantly lower and represented the levels in sediments measured in lakes of Kola Peninsula located further off from industrial pollutant sources. An exception was Pb the concentration of which was at the same level as in Lake Imandra, probably due to long-distance transport. Sediment layers were subjected to four-step sequential extraction procedure to reveal the metal distribution in soluble, exchangeable, acid-soluble, and residual fractions. Indicative of their potential higher lability, Mn, U, and Zn were generally found in exchangeable fraction; as also Mn and U extensively in the acid-soluble fraction.

Elefsis gulf, on the coasts of Attiki, in Greece, is characterised by its rather enclosed type, the presence of heavy industries located at its northeastern coast (like refineries, shipyards, iron and steel industries) and the use of its ports for the transportation of raw material and products. Previous research has shown that both industrial and marine transport activities, during the past six decades, have contaminated the gulf environment with various pollutants including metals. The respective sedimentation rate was calculated to approximately 0.5 – 0.8 cm/year. The present work is aiming to evaluate Cu, Zn and Sn vertical and fractional distribution in Elefsis gulf sediments. For this purpose, sediment cores were collected from four sites along the north coast of the gulf. After lyophilization and sieving, the samples were treated applying the sequential extraction analytical procedure of Tessier et al (with a few modifications) for the partitioning of the elements among the various geochemical fractions. Metal concentrations were measured using Atomic Absorption Spectroscopy. The results showed that most of the non-residual Cu is associated with the organic/sulphides fraction, as Cu exhibits a strong affinity for the organic matter while it can also be present in sulphide minerals. In general, significant Zn percentage is associated with the exchangeable fraction (12% - 32% of the total), indicating biological availability and anthropogenic input. As expected, considerable Zn is bound to ferromanganese oxides (21% - 41% of the total) due to their scavenging ability for trace metals. The four non –residual fractions of Zn show a downcore decrease. More than 79% of the total Sn occurs in the residual fraction. However, the four non-residual fractions of Sn exhibit enrichment at 10-20 cm sediment core depth. Concluding, Elefsis gulf sediments correspond to a significant pollution level while the recent ones may act as secondary pollution sources, implying therefore the need for an environmentally sound management scheme.

The influence of texture on the mechanical response of commercial purity copper sheet in some simple forming processes

Worldwide, crystal plasticity models are currently developed to predict texture development during processing of material. Such models require a precise knowledge of the active deformation mechanisms. The activation energy for certain deformation modes will change with temperature and also depend on the chemistry of the alloy as well as the microstructure. Deformation mechanisms were studied in ZIRLO™ during room and high-temperature uniaxial compression testing. Materials with a strong crystallographic basal texture and a more random texture due to β-quenching were investigated with the aim of establishing the effect of temperature, microstructure, and texture on the active deformation modes during the initial stages of deformation. First, specimens were strained at room temperature, 180°C and 300°C to 2 % and 5 % or 10 % total strain and subsequently analyzed by Electron Back Scatter Diffraction (EBSD) to determine the texture evolution. It was found that a dramatic texture change was observed for all testing temperatures in the strongly textured specimen after only 5 % total strain, which can only be understood in terms of tensile twinning of {10 1¯2} ⟨1¯011⟩ being active mainly at room temperature and compressive twinning of {11 2¯2} ⟨1¯1¯23⟩ being operational at room and elevated temperature. The β-quenched specimens did not show any evidence of texture change when strained to 10 %. In-situ intergranular strains were measured by time-of-flight neutron diffraction during continuous compressive loading. This information enabled the development of a crystal plasticity finite element model (CPFEM), which was subsequently used to predict the stress state in individual grains. It was found that in the strongly textured material the spread of intergranular strain in the {0002} grain family (normal pointing towards the ND direction) results in some grains being in compression even though the mean stresses are tensile, which could explain the activation of the observed compressive twinning. The crystal plasticity model also demonstrated that the observed texture changes in the strongly textured material, including those at high temperature, cannot be explained by slip alone even when ⟨c+a⟩ slip is considered. In addition, the model showed that the dramatic difference in yield strength of the two conditions studied here cannot be solely attributed to the difference in texture but that grain size plays an important role.

Worldwide, crystal plasticity models are currently developed to predict texture development during processing of material. Such models require a precise knowledge of the active deformation mechanisms. The activation energy for certain deformation modes will change with temperature and also depend on the chemistry of the alloy as well as the microstructure. Deformation mechanisms were studied in ZIRLO™ during room and high-temperature uniaxial compression testing. Materials with a strong crystallographic basal texture and a more random texture due to β-quenching were investigated with the aim of establishing the effect of temperature, microstructure, and texture on the active deformation modes during the initial stages of deformation. First, specimens were strained at room temperature, 180°C and 300°C to 2 % and 5 % or 10 % total strain and subsequently analyzed by Electron Back Scatter Diffraction (EBSD) to determine the texture evolution. It was found that a dramatic texture change was observed for all testing temperatures in the strongly textured specimen after only 5 % total strain, which can only be understood in terms of tensile twinning of {101¯2} ⟨1¯011⟩ being active mainly at room temperature and compressive twinning of {112¯2} ⟨1¯1¯23⟩ being operational at room and elevated temperature. The β-quenched specimens did not show any evidence of texture change when strained to 10 %. In-situ intergranular strains were measured by time-of-flight neutron diffraction during continuous compressive loading. This information enabled the development of a crystal plasticity finite element model (CPFEM), which was subsequently used to predict the stress state in individual grains. It was found that in the strongly textured material the spread of intergranular strain in the {0002} grain family (normal pointing towards the ND direction) results in some grains being in compression even though the mean stresses are tensile, which could explain the activation of the observed compressive twinning. The crystal plasticity model also demonstrated that the observed texture changes in the strongly textured material, including those at high temperature, cannot be explained by slip alone even when ⟨c+a⟩ slip is considered. In addition, the model showed that the dramatic difference in yield strength of the two conditions studied here cannot be solely attributed to the difference in texture but that grain size plays an important role.

Sheets of the Al-Mg-Si alloy AA6016 have been prepared with different microstructures by rolling and annealing, followed by heat treatment to the T4 condition. These have been biaxially stretched using the Marciniak driving blank method, and their limit strains measured. Such biaxial stretching limits are very sensitive to inhomogeneity with length scales greater than about half the sheet thickness, and significant factors in that inhomogeneity are the materials grain size and the spatial segregation of texture. In this material, it appears that colonies of cube textured grains have an effect on the limit strains. However, there is significant change of texture during stretching and this texture evolution also needs to be considered. Finite element modelling has been used to evaluate the effects of grain size, clustering of the initial texture and texture evolution on the biaxial stretching limits.

This paper reports an investigation on the evolution of texture and plastic anisotropy during uniaxial tensile testing of extruded profiles produced from two variants of an AlZnMg alloy: one contains Zr and shows a non-recrystallized structure; the other is Zr-free and shows a recrystallized structure. Tensile tests were carried out at 0°, 45° and 90° from the extrusion direction and from which, experimental r-values were derived from quadratic polynomial functions fitting to the width and thickness strains in the tensile tested samples. The r-values and Taylor factors for the initial and tensile tested samples were simulated from the measured textures using the full constraints and relaxed constraints Taylor models. The results show remarkable differences in textures and anisotropy in the two profiles. Although the initial textures of the profiles are much sharper, the texture development in the tensile tests follows similar tendencies commonly observed in sheet metals. In general, the r-values predicted from the textures depict the same tendencies of variation with tensile strain as those for the experimental r-values, suggesting that the variation of plastic anisotropy is mainly caused by the texture evolution. The Taylor factors were used to simulate the in-plane anisotropy in yield strength and subsequent work hardening. For the latter, a better agreement with the experimental data was obtained when the texture changes due to tensile deformation was taken into consideration.

This study investigates the local texture modification of two magnesium alloys (AZ31 and ZX10) and an aluminum alloy (AA6082) based on changes in the die design. For this purpose, a conventional flat die and a modified die, which has been additively manufactured to allow for a significant modification of the material flow, are investigated. Extrusion tests are carried out, followed by a comprehensive examination of the microstructure and local texture development. These experimental results are complemented by finite element analysis of the state variable distribution in the cross section of the extruded band. The results demonstrate that the texture change is connected to the strain path and can therefore be controlled based on the die design. This equally applies to all of the investigated alloys, despite their differences in crystallographic deformation and recrystallization behavior. Accordingly, a rotation of the dominant texture components about ND at the edge of the band of approximately 40°, 45°, and 20° is observed for AZ31, ZX10, and AA6082, respectively. These findings correlate well with the difference in rotation around ND between the dies of 39°, which is calculated numerically based on the deformation gradient tensor. Furthermore, AZ31 and ZX10 demonstrate a broadening of the basal planes in the TD when extruded with the modified die, which can be related to the increased shear strains in the ED/TD plane over the entire width of the band. For ZX10 specifically, a completely different texture is generated due to the combination of the broadened basal planes in TD, the rotation of the dominant texture component around ND, and its tilt in ED, characteristic of extruded Ca-containing Mg-alloys. The investigation on AA6082 further illustrates the importance of the effective temperature and strain rate in the forming zone for its texture development. While no significant change in the microstructure is evident, the increased heat dissipation and smoothed introduction of dislocations during extrusion with the modified die correlates with a transition from Cube to Goss as the dominant texture component.

The effect of strain path on microstructure and texture development in copper single crystals with (110)[001]and (110)[11̄0]initial orientations

During friction stir welding (FSW), a cylindrical threaded tool pin rotates and plunges into the workpieces and produces a stirring action that joins the workpieces together, while the shoulder part of the tool forges down the workpiece providing frictional heating. The joining is accomplished by running the rotating tool along the weld line. Significant heat is generated mainly from the friction between the tool shoulder and workpiece, while a severe plastic deformation occurs in the softened material by the stirring pin. As a result, a severely-deformed ‘stir zone’ with fine grains is produced through dynamic recrystallization (DRX). To date, the challenge remains in the fundamental understanding of the governing mechanisms for the grain refinement, texture formation, and the resulting mechanical behavior after FSW of Mg alloys. It is noted that, for hcp crystalline structure, deformation condition dominates the active deformation modes (slip vs. twinning), and, hence, the development of texture [1]. In this study, the objective was to investigate the influence of thermo-mechanical input during FSW on texture development and the corresponding mechanical behavior after FSW of AZ31B Mg alloy. A series of FSW experiments were designed to cover a wide range of deformation conditions by varying the rotation and travel speeds of the tool. Subsequently, the changes in texture of the stir zone were investigated using neutron diffraction technique. The tensile behavior of the FSW plates was also examined. Finally, the relationship among the processing parameters, texture evolution, and the mechanical behavior of the FWP Mg alloy plate is discussed.KeywordsFriction Stir WeldingFriction Stir WeldingFriction Stir ProcessingTexture DevelopmentWeld LineThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Despite a tremendous amount of research to understand the evolution of microstructural and texture changes during deformation, there is still a need for further deep insight into it. The most used deformation process underuse in industries is the rolling of material. Stacking fault energy is the most critical material property, which governs the deformation behavior. In the present study, the microstructure and texture changes of a high SFE material (pure nickel) during cold rolling was investigated. The objective is to find criteria for the change of orientation of a particular grain as rolling proceed. Pseudo-in-situ rolling was done through which the shape, orientations, and neighbors of each grain could be tracked as a function of rolling reductions. It was found that orientations of some grains remain stable after a large reduction and do not develop sub-grains within it, whereas orientations of some grains change drastically at a very low deformation level along with the evolution of a large number of sub-grains.